A couple questions I didn't get

I did several pages of calculus for homework, and these are the questions I got stuck on:

1. Find the derivative of y=2/√x + x/√3 + 6(x)^1/3.

2. Find the derivative at x= -2 for y=3u²+2u and u = √(x²+5).

3. The amount of pollution in a certain lake is P(t) = (t^0.25 + 3)³, where t is years and P is parts per million. What is the rate of change after 16 years (I know I use the limit formula but the exponents and t+h are confusing me).

4. Find the x-intercept of the function f(x)= 2x^(5/3) - 5x^(2/3).

5. If f is a differentiable function, find an expression for the derivative of h(x)=2xf(x).

Thanks! (Yes)